Metal hydride bands and use thereof for storing hydrogen

ABSTRACT

The invention concerns a piece based on one or several metal hydrides capable of reversibly absorbing hydrogen. Said piece is in the form of a thin and dense band, having a thickness preferably not more than 1 mm and porosity preferably less than 20%. The piece is obtained by rolling a powder of selected hydride(s), with or without additional component(s), such as binders or heat-transfer elements. Said piece can easily be produced on an industrial scale. By its very nature, it is particularly adapted for use as a base element in a tank for storing and transporting hydrogen. It can also be used in a Ni-MH typre battery for storing and transporting energy.

BACKGROUND OF THE INVENTION

The present invention relates to pieces made of at least one metalhydride, which are in the form of strips obtained by rolling.

The invention also relates to the use of these pieces for the storageand transportation of hydrogen in hydrogen storage tanks.

The invention further relates to the use of the same pieces in batteriesof the Ni-MH type and in equipment used for purification, separation,compression, detection, cooling, heating, storing and generation ofenergy.

In the present description and the appended claims, the expression“metal hydrides” is used to designate all metals, alloys, composites andother materials known to absorb hydrogen in a reversible manner, whetherthese products are in a non-hydrogenated form (that is before absorptionor after desorption of hydrogen) or in a hydrogenated form (that isafter absorption and before desorption of hydrogen). These hydrides canbe of the type known to be “high temperature”. By way of examples ofsuch hydrides, mention can be made to Na, Mg, Mg₂Ni, Li, Ti, Zr and Ca.These hydrides may also be of the type “low or relatively lowtemperature”. By way of examples of such hydrides, mention can be madeto MmNi₅, LaNi₅, CaNi₅, FeTi, Ti_(0.98)Zr_(0.02)V_(0.43)Fe_(0.09)Cr_(0.051) Mn_(1.5) and the Bogdanovic alloys.

BRIEF DESCRIPTION OF THE PRIOR ART

The use of metal hydrides for storing and transporting hydrogen is wellknown per se. The hydrogen which is so stored is usually used as asource of energy for hydrogen powered vehicles, batteries or machines orother kind of equipments used for purification, separation, compression,detection, cooling and heating.

If all these potential applications are extremely interesting, there isstill a practical problem of heat and mass (hydrogen), transfer which isassociated to the use of metal hydrides having high hydrogen absorptionand desorption kinetics. Indeed, absorption of hydrogen by a metalhydride is an exothermic phenomenon. Therefore, it is necessary toquickly evacuate the heat during the absorption, since otherwise theprocess will be slowed down. On the other hand, desorption is anendothermal phenomenon. It is therefore necessary to provide heat in aquick manner in order to extract hydrogen at a high rate from a metalhydride. When one wants to hydrogenate or dehydrogenate very quickly amaterial and thus, at the same time, to extract or supply heat, thethermal and diffusion paths must be reduced as much as possible, therebymaking it necessary for the material to have at least one dimensionwhich is small. Moreover, in order to obtain a high storage capacity pervolume unit, it is necessary to consolidate and densify the hydride whenthe latter is in the form of a powder.

In order to tentatively overcome this problem, Japanese patentapplication No. JP-A-60/262.830 published on Dec. 26, 1985 in the nameof TOYOTA CENTER OF RESEARCH & DEVELOPMENT LAB suggests to give theshape of a thin sheet to the hydride. This sheet is obtained by“molding” the hydride around a metal mesh by means of a synthetic resin,such as a silicon resin. Such a “molding” process is quite difficult tocarry out from an industrial standpoint. Moreover, as everybody knows,synthetic resins (polymers) cannot be exposed to high temperatures.Accordingly, the hydrides that can be used can only be low temperaturemetal hydrides (example 1 of this laid-open application refers toLaNi₅). It is impossible to use this technology with high temperaturemetal hydrides. Moreover, since synthetic resins do not conductelectricity and heat, it is necessary to incorporate heat pipes into themolded sheet in order to circulate a heating/coding fluid for heatexchange.

OBJECTS AND SUMMARY OF THE INVENTION

A first object of the present invention is to give to a metal hydride aform suitable to efficiently solve the practical problem of heat andmass transfers mentioned hereinabove.

A second object of the invention is to achieve the requested forming ofa metal hydride by using a technology that can easily be carried out inmass production and at low cost.

A third object of the invention is to generalize the use of metalhydrides that are so formed to all possible industrial applications forthis type of product known to be capable of absorbing hydrogen inreversible manner.

In accordance with the invention, these various objects are achievedwith at least one piece made of at least one metal hydride capable ofabsorbing hydrogen in a reversible manner, said piece being in the formof a thin and dense strip obtained by rolling of a powder of said atleast one metal hydride and being characterized in that said strip isobtained at a temperature lower than 400° C.

This piece preferably has a thickness equal to or lower than 1 mm andmade from a powder metal hydride(s) of nanocrystalline structure(cristallites of a size lower than 100 nm). This piece can have anyshape: straight, stacked, folded, spiral, curved, twisted or cut.

In accordance with a particularly preferred embodiment of the invention,this piece may contain a first additional component for supplying and/orevacuating heat. This first additional component may also act as abinder for the powder of metal hydride(s).

The piece may also contain a second additional component acting as abinder for the powder of metal hydride(s).

The first end/or second additional components are preferably in the formof a powder additive. This additive may be a powder of Mg, Cu or Al.

Alternatively, the first and/or second additional components may be inthe form of a tridimensional matrix preferably made of metal and havingporous structure, that is rolled together with the powder of metalhydride(s).

The first and/or second additional components may also be in the form ofa plate or tube in direct contact with the powder of metal hydrides).

Preferably, the weight of the first and/or second additional componentscorresponds to a maximum of up to 50% of the weight of the whole piece.More preferably, this weight does not exceed 30% only of the weight ofthe whole piece.

Intrinsically, the piece according to the invention is capable ofabsorbing hydrogen in a reversible manner. It can be formed to haveintrinsic electric characteristics allowing measurement of its hydrogencontent. It can also be formed to have intrinsic electriccharacteristics allowing desorption of hydrogen by circulation of anelectric current.

As indicated hereinabove, the piece made of metal hydride(s) accordingto the invention is manufactured by rolling. This process isparticularly advantageous in that it allows the manufacture of verydense strips of a very small thickness which as a result, have theabove-mentioned characteristics. This process also has the advantage ofbeing perfectly adapted for industrial production on a large scale andat low cost.

Because of its property, the piece according to the invention isparticularly well adapted for use as basic components in a tank for thestorage and transportation of hydrogen. It can also be used in a batteryof the type Ni-MH for the storage and transportation of energy. It canfurther be used in other equipment selected amongst the purification,separation, compression, detection, cooling, heating, storing andgeneration of energy.

The invention and its advantages will be better understood upon readingthe following more detailed but non-restrictive description made inreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the manufacture of a piece ofmetal hydride according to the invention, incorporating a tridimensionalporous metal structure;

FIG. 2 is a representation of a piece of metal hydride according to theinvention, associated with, on the one hand, a metal plate used as aheat carrier (and possibly as a contact electrode) and, on the otherhand, mattresses of porous fibers for the supply and removal of hydrogenand for volume compensation;

FIG. 3 is a cross-sectional view of an ensemble consisting of a pieceaccording to the invention associated with, on the one hand, a metalplate acting as a heat carrier and, on the other hand, an insulatingmattress, said figure giving numerical simulation of the heat transferin this ensemble during hydrogen absorption;

FIG. 4 is a curve illustrating the variation of resistivity of aconsolidated piece of a metal hydride of the formula MgH₂-5 at. % Vduring hydrogen desorption and the variation of differential pressure ofthe hydrogen titration apparatus, as a function of the temperature;

FIG. 5 is a schematic cross-section view of a tank for storing hydrogen,comprising a stack of pieces according to the invention;

FIG. 6 is an open perspective view of the tank shown in cross-section inFIG. 5; and

FIG. 7 a to 7 d are perspective views showing in a schematic manner,different shapes that may have the pieces according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

As previously indicated, the invention essentially relates to a piecemade of one or more metal hydrides that are capable of absorbinghydrogen in a reversible manner. The piece is in the form of a thin anddense strip having a thickness preferably equal to or lower than 1 mmand a porosity preferably lower than 20% which is obtained by rolling apowder of the selected hydride(s) with or without additionalcomponent(s). This strip has a typical width which is preferably lowerthan 15 cm and a length that can be of several meters.

By way of non-restrictive examples of hydrides that can be used for themanufacture of the pieces, mention can be made to those ofnanocrystalline structures disclosed in U.S. Pat. Nos. 5,763,363;5,837,030; 5,872,074 and 5,906,792 either in the name of the Applicantalone or in the name of the Applicant and the McGill UNIVERSITY. Evenmore particularly mention can be made to Mg.-based hydrides.

The key feature of the invention lies in the use of the well knownmethod of “rolling” for giving to the powder of hydrides the form ofthin and dense strips and thus for allowing optimization of thetransfers of mass (hydrogen) and heat involved during the process ofabsorption/desorption of hydrogen.

In order to obtain by rolling having a high structural integrity,additional components such as binders can be added as additives to thehydrides. By way of examples of such additives, reference can be made toMg, Al, V, Cu, Li, Fe, Nb, C, graphite, Co, Ni, Mn, Cr, Ti, Zr, andFeTi. These additives are preferably in the form of a powder that can bemixed with the powder of hydrides(s) and rolled together with it.

As an additional component, it may also be suggested to use atridimensional structure preferably porous and made of metal, such as ametal foam, to insert the metal hydride powder into the pores of thestructure and to roll the whole to obtain a thin strip. The metalstructure that is so incorporated to the piece then permits to morequickly remove heat from the strip during hydrogen absorption.

FIG. 1 is illustrative of this process of manufacture. As is shown, thetridimensional metal structure 3 is introduced with a carrier plate 5preferably made of a heat conductive material, between the rollers 7 ofa rolling machine. Just before such an introduction, the powder of metalhydride 9 stored into a tank 11 is poured into the structure 3 to fillup its pores. After rolling, the so obtained piece in the form of a thinand dense strip 1 can then be combined with other elements such as anelectrical contact grid 13 and mattresses 15 of micro glass-fibers inorder to obtain an operating unit ready to be incorporated into a tankfor the storage of hydrogen.

In use, the rolling step can be carried out at ambient temperature or atelevated temperature (lower than 400° C.). The rolls 7 can be heated andtheir relative position can be adjusted to obtain a requested thicknessand density.

As can be understood, the above-mentioned additives are used and rolledwith the powder of metal hydride essentially in order to give structuralintegrity to the strip and to act as a heat conductor. Accordingly, itis important to preferably use additives in the form of metal powders ormetal fibers, which are capable of acting not only as binders but alsoas heat conductors.

Together with these additives or as substituents for them, use can alsobe made of the tridimensional metal structure, or of the carrier plateor grid as already referred to hereinabove, or also of a metal tube intowhich the hydride powder is inserted before the rolling step. Thesecomponents should also be made of a heat conductive material and bepreferably provided with holes to let flow the hydrogen to be absorbedor desorbed.

In order to promote the desorption of hydrogen, use can be made of theintrinsic electric characteristics of the pieces in the form of stripsobtained by rolling. Thus, for example, it is known that magnesiumhydride MgH₂ is an insulating material. When the content of metaladditives in a form of a powder or in a form of porous structure exceedsthe percolation point, a strip made from this hydride becomesconductive. Moreover, during the desorption, MgH₂ switches from aninsulating state to a conductive state. Thus, use can be made of thesecharacteristics to induce desorption of hydrogen from the strip bypassing an electric current therein. The change of resistivity of thepieces as a function of the content of hydrogen contained in them mayalso be used as an indicator of the amount of hydrogen within the tank.

FIG. 4 illustrates as an example, the change of resistivity of aconsolidated piece made of MgH₂ and the change of differential pressureof the hydrogen titration apparatus used for measuring the amount ofhydrogen within this piece as a function of the temperature during adesorption step. This figure shows that, during desorption, magnesiumhydride (MgH₂) which is an insulating material, becomes conductive (Mg).This figure can be associated to the table given below which indicatesthe value of the electric resistance of 1 mm thick rolled pieces madefrom the same nanocrystalline metal hydride of formula MgH₂-5 at % V, towhich were added variable amounts of a binder consisting of Mg ofgranulometry ranging from 105 μm to 850 μm (the Internal resistance ofthe measurement apparatus was 2000Ω).

Amount of binder (Mg) added (expressed in weight) 0% 10% 15% 20% 30%Measured 4 × 10¹⁰ 1 × 10¹⁰ 3000 <2000 <2000 resistance (Ω)

It will be noticed that when the additional component acting as a binderis in the form of a powder that is mixed with and integrated to thehydride powder, it is of the highest importance that this component bewell distributed and occupy all the volume of the piece, as is the caseof a tri-dimensional metal structure when it is inserted into thehydride powder during rolling (see FIG. 1). As a matter of fact, oneand/or the other of these two solutions are very preferable to a merepressing of the hydride powder onto a substrate without any additives.

The concept of using pieces in the form of rolled strips of metalhydrides prepared as disclosed hereinabove, is sufficiently flexible tobe adapted to a multitude of applications. These strips may be of anyshape. They may be flat and rectilinear strips, cut into straightsections (see FIGS. 5 and 6. Alternatively, the strips may be folded andstacked upon themselves (FIG. 7 a), rolled in a spiral (FIG. 7 b),curved (FIG. 7C) or cut, sectioned and reassembled at an angle (FIG. 7d).

FIGS. 5 and 6 illustrate a possible use of several pieces 1 in the formof straight strips into a tank 21 for the storage and transportation ofhydrogen. The tank 21 comprises an external wall 23, an internal wall 25fixed to the external wall via a corrugated sleeve 27 acting as amechanical reinforcement and a thermal breaking. Thanks to itsstructure, the sleeve also defines a plurality of conducts 29 for a heatcarrying fluid (water, oil or any other liquid) which is brought at 31and used for cooling during the absorption or for heating during thedesorption of hydrogen. The hydrogen circulates via a pipe 33 openinginto the container which is defined by the internal wall 25 and in whichthe pieces 1 are stacked. Contact plates 5 perforated with holes, act asheat carriers and are connected to the internal wall to act togetherwith it as a heat exchanger. Mattresses of glass microfibers having aporosity of, for example, 90% with pores of, for example, 0,3 microns,are positioned between the pieces as shown in FIG. 2, to ensure thesupply and removal of hydrogen and to absorb volume dilatation orcontraction.

The tank 21 disclosed hereinabove, has numerous advantages. It is safeand of easy operation. It is easy to fill and of a great capacity. Itallows liberation of hydrogen upon request, and such in a very efficientand fast manner thanks to the structure of the pieces 1 and theirspacing. The absorption/desorption kinetics are very fast and thestorage capacity is very high. The number of cycles ofabsorption/desorption is also high.

Such makes the tank 21 useful in the field of transportation (cars,buses, tractors, trucks, recreation vehicles, planes, boats, trains,military transports, etc . . . ) or for the manufacturers/users of fuelcells, the producers of decentralized energy, the users of hydrogen ofvery high purity and the users of filters for hydrogen.

So far, in all the applications involving hydrogen especially as asource of energy for fuel cells or internal combustion engines or assources for the production of hydrogen in reformers or electrocatalicmachines, the storage of hydrogen was done either under very highpressure with the safety problem that such generates (pressure >>300psi), or in liquid form, with the problems of the storage at very lowtemperatures (<−253° C.). Another solution is the use of conventionalhydrides in the form of a non compacted powder or of massive pieces withthe problems that such generate, in particular, a very lowabsorption/desorption kinetics and a low storage capacity.

The use of rolling as proposed according to the invention for themanufacture of thin and dense strips of hydrides, permits to optimizethe absorption/desorption kinetics in storage tanks and to maximize theheat transfer. The use of the intrinsic electric properties of theconsolidated strips close to the percolation point, permits to measurethe content of hydrogen and promote the desorption of hydrogen. Becauseof their structure, the so-obtained pieces permit to optimize mass andheat transfer within the tanks of metal hydrides. It provides largehydrogen absorption/desorption kinetics, fast mass and heat transfer andhigh number of cycles of absorption/desorption. Also because of theirstructure, the consolidated pieces are safe as compared to a powder ofnon-binded hydride which presents a certain level of pyrophoricity.

The technology disclosed hereinabove and the pieces of hydride(s) in theform of strips according to the invention may also be used efficientlyfor applications in batteries of the Ni-MH type (nickel-metal hydride).

The field of application of the hydride strips and the hydrogen storagetanks using these pieces in the form of rolled hydride strips accordingto the invention is therefore very wide. This technology is particularlywell adapted for use with nanocristalline hydrides since these materialshave very high hydrogen absorption and desorption kinetics. It isparticularly well adapted for the Mg-containing hydrides (Mg, Mg₂Ni andthe related materials), Li, Na, Ti, Zr and Ca, which are known to be“stable” hydrides operating at a high temperature and for which theproblem of heat exchange is important. This technology may also be usedwith low temperature hydrides such as MmNi₅, LaNi₅, CaNi₅, FeTi,Ti_(0.98), Zr_(0.02), V_(0.43), Fe_(0.09), Cr_(0.05), Bogdanovic alloys,etc., that is, in summary, with all hydrides of the AB₅, AB₂, AB, A₂B,types, solid solutions, nanocrystalline and amorphous alloys, complexhydrides and even carbon, nanotubes, etc.

1. A piece comprising at least one metal hydride capable of absorbinghydrogen in a reversible manner, said piece being in the form of a thinand dense strip obtained by rolling a powder of said at least one metalhydride, wherein said powder of said at least one metal hydride isnanocrystalline said strip being obtained at a temperature lower than400° C.
 2. The piece according to claim 1 further comprising a firstadditional component for heat-related actions selected from the groupconsisting of supplying heat and evacuating heat.
 3. The piece accordingto claim 2, wherein said first additional component is a binder for thepowder of said at least one metal hydride.
 4. The piece according toclaim 1 further comprising a second additional component which is abinder for the powder of said at least one metal hydride.
 5. The pieceaccording to claim 4, wherein at least one of said first and said secondadditional components is in the form of a powder additive.
 6. The pieceaccording to claim 5, wherein said powder additive comprises Mg.
 7. Thepiece according to claim 4, wherein at least one of said first and saidsecond additional components is in the form of a tridimensional matrixthat is rolled together with the powder of said at least one metalhydride.
 8. The piece according to claim 7, said matrix comprises metalhaving a porous structure.
 9. The piece according to claim 4, wherein atleast one of said first and said second additional components is in theform of a plate in direct contact with the powder of said at least onemetal hydride.
 10. The piece according to claim 4, wherein at least oneof said first and said second additional components is in the form of aplate in direct contact with a tube selected from the group consistingof a tube containing said at least one metal hydride and a rolled tubecontaining said powder of said at least one metal hydride.
 11. The pieceaccording to claim 4, wherein at least one of said first and said secondadditional components are up to 50% of the weight of the whole piece.12. The piece according to claim 11, wherein at least one of said firstand said second additional components are up to 30% of the weight of thewhole piece.
 13. The piece according to claim 1, said strip having athickness equal to or less than 1 mm.
 14. The piece according to claim 1wherein said at least one nanocrystalline metal hydride comprises MgH₂-5at. % V.
 15. The piece according to claim 1 wherein said strip is of ashape selected from the group consisting of straight, stacked, folded,spiral, curved, twisted and cut shapes.
 16. The piece according to claim1, said piece being formed to have intrinsic electric characteristicsallowing measurement of its hydrogen content.
 17. The piece according toclaim 1, said piece being formed to have intrinsic electriccharacteristics allowing desorption of hydrogen by circulation of anelectrical current.
 18. A method for storing and transporting hydrogenin a tank, comprising use of a piece according to claim
 1. 19. A methodfor stocking and transporting energy in a battery of the Ni-MH type,comprising use of a piece according to claim 1.